TheWavefront Ontology: Time as Causal Determination, Not Geometric Dimension

We propose the Wavefront Ontology, a formal framework for temporal presentism in which physical reality exists exclusively at the present moment and time is the process of causal determination rather than a geometric dimension. The paper introduces five principal contributions: the Sandwich Principle (a theorem of forward causal inescapability), a burden of proof inversion establishing that the block universe bears the evidentiary burden for its extraordinary ontological claims, the 4+1D shadow interpretation of relativistic spacetime, a rigorous information-theoretic arrow of time, and a Born rule derivation from the determination process via Gleason's theorem. The framework connects to causal set theory and identifies experimental predictions including gravitational decoherence and quantum Zeno granularity.